Drill collar with cutting surface



Sept. 26, 1967 w. M. TERRY DRILL COLLAR WITH CUTTING SURFACE Filed Aug. 15, 1966 INVENTOR. (El/0'00 any? United States Patent 3,343,615 DRILL COLLAR WITH CUTTING SURFACE William M. Terry, Houston, Tex., assignor to Esso Production Research Company Filed Aug. 15, 1966, Ser. No. 572,568 7 Claims. (Cl. 175-406) ABSTRACT OF THE DISCLOSURE A finned drill collar forms a cross in horizontal crosssection and has hard, abrasive-faced fins perpendicular to the next adjacent fin extending the length of the drill collar and provides passageways for fluid; this allows greater penetration rates in air drilling at reduced bit rates and reduction in wall sticking when using liquid drilling fluids.

This application is a continuation-in-part of Ser. No. 356,834, now abandoned, entitled Drill Collar, filed Apr. 2, 1964, for William M. Terry.

The present invention is directed to a drill collar having a cutting surface. More particularly, the invention is concerned with a drill collar for use in a drill string having a drill bit forming a part thereof. In its more specific aspects, the invention is concerned with a drill collar of a particular configuration for employment in a drill string.

The present invention may be briefly described as a drill collar comprising an elongated member adapted to be arranged in and made part of a drill string. The elongated member is provided with longitudinally and radially extending fins arranged to form a cross in horizontal cross section having a cutting surface on the outer periphery thereof. The fins extend longitudinally substantially the length of the elongated member. The elongated member has a fluid passageway extending therethrough for circulation of drilling fluid.

The outer cutting surface of the fins may be convex relative to the longitudinal axis of the elongated member and this surface may be faced with a hard, abrasive material such as tungsten carbide, diamonds, carborundum, carbonized steel, and the like to aid in cutting.

The longitudinally extending fins extend radially from the member a distance slightly less than the gauge of the drill bit which forms a part of the drill string. This distance may be within the range from about inch to about inch less than the gauge of the drill bit forming part of the drill string and thus less than the gauge of the well drilled by the bit. The fins have a cross-sectional thickness within the range from about one-half to about twice the diameter of thefluid passageway.

The present invention is particularly useful in air or gas drilling but may be employed in any drilling operation, such as air or gas drilling where air or gas is used as the drilling fluid or where a liquid is employed as the drilling fluid.

It has been determined that the penetration rate in drilling operations, where air or gas is the drilling fluid, is improved by an increasing the air or gas velocity below the bit. This velocity is in inverse proportion to the absolute pressure of the gasiform drilling fluid below the bit, the minimum value of which is limited by the frictional pressure drop of the gasiform fluid. Cuttings flow from the bit to the surface through the annular space between the borehole wall and the drill pipe or drill collars. The amount of pressure drop due to friction depends upon the shape and size of the flow passage between the drill string and the wall of the borehole and may be expressed as a function of the equivalent diameter of the flow passage as calculated from the mean 3,343,515 Patented Sept. 26, 1967 hydraulic radius of the passage. An increase in equivalent diameter results in a decrease in frictional pressure drop. The drill collar of the present invention provides flow passages of greater equivalent diameter than those obtained with drill collars of the prior art. This results in a higher gasiform fluid velocity at the bit because the frictional pressure drop along the drill collars is less and gives a greater penetration rate in drilling operations.

It has been determined that 51% of the annular pressure drop in a 7 /8" hole was across 358 feet of 6.07" round drill collars wtih the bit at a depth of 3294 feet. At 5005 feet, 36% of the pressure drop occurred across the same collars. In comparison with these pressure drops, the air velocity at the bit at these same depths, while employing the present invention, will result in velocities of the drilling fluid 49% and 31% greater, respectively, employing the same length of drill collars of the present invention. An increase of this magnitude in air velocity will result in a signaficant increase in drilling rate.

The present invention will be further illustrated by reference to the drawing in which:

FIG. 1 is an isometric view of the drill collar; and

FIG. 2 is a top view of the drill collar of FIG. 1.

Referring now to the drawing wherein a preferred embodiment is illustrated, numeral 11 designates an elongated member provided with four longitudinally and radially extending fins 12 which are spaced apart horizontally and equidistantly, each fin being perpendicular to the next fin as shown in the drawing. The elongated member 11 is provided with a fluid pasageway 13 extending therethrough for circulation of drilling fluid. The upper end of the fluid passageway is provided with threads 14 for receiving a threaded pin of a corresponding drill collar or a portion of the rotatable drill string used in drilling a borehole. The lower end of the drill collar is provided with a threaded pin 15 for insertion into and threaded connection with the drill string or to another drill collar forming part of the drill string.

The outer cutting surfaces 16 of the fins 12 may be convex relative to the longitudinal axis of the elongated member 11 and these surfaces may be faced with a hard, abrasive material such as tungsten carbide, diamonds, and. the like; It is also contemplated that the hard, abrasive material may be extended to cover the bottom surface of the fins to provide a cutting surface or facing 16A which may serve as a reamer or hold opener if the drill bit wears under gauge. Increased torque resulting from such reaming action may be observed by the drilling personnel at the surface as an indication that the bit has become worn and should be replaced.

Referring now to FIG. 2, the fluid passageway or water course 13 is shown in a typical example as having a diameter of about 1 /2". In this particular case, the fins 12 may have a cross-sectional thickness from about 1" to about 2" or more, as required by the average drilling conditions under which the drill collars may be used, as the case may be. The outer cutting surface of the free ends of the fins is provided with a hard facing 16 of tungsten carbide. The dimensions shown in FIG. 2 are dimensions employed for a drill collar to be used with a 7%" bit and the diameter of the gauge of the drill collar lar will be 7 5 with fins having a width of either 1" or 2".

The drill collar described with reference to FIGS. 1 and 2 has a stiffness comparable to the square drill collar of the prior art and provides for greater flow of gasiform fluid than the prior art and thus permits maximum penetration rates of the drill bit in areas where crooked holes ordinarily result. This is accomplished because the drill collar of the present invention allows significantly higher penetration rates where hole deviation requires long periods of drilling with a light weight on the bit. Also, by providing the cutting surfaces 16, it is possible to ream out any key seats which result from deviated or crooked holes.

The following Table I illustrates comparable characteristics of different types of drill collars in sizes normally run in 7 /5" holes:

Norm-The last two drill collars are drill collars of the present inveution.

It will be clear from the data in Table I that the drill collar of the present invention provides greater space with the wall of a well than the prior art devices. Thus, the 6" round drill collar in a 7 /8" hole does not provide as much space as the present drill collar. The same holds true for the square drill collar. It will be apparent that the ratio of cross-sectional area to equivalent diameter of annulus (space) for the two drill collars of the present invention are, respectively, about 13:1 and about 4:1. It is therefore contemplated that drill collars providing ratios of about 3:1 to about 15:1 may be employed.

The lengths shown in Table I are provided for comparison purposes only since the actual length of collars used in a well depends on how much weight the driller wishes to run on the bit. It will be manifest, however, that the required length of a drill collar in accordance with the present invention with a 1" thick fin is approximately twice that of the other three drill collars. However, the increased air velocity obtained with the drill collar of the present invention permits greater penetration rates at reduced bit weights so that the optimum collar length may be reduced.

The present invention is also quite advantageous where it is used with liquid drilling fluids since the drill collar of the present invention has less contact with the wall of the hole which greatly reduces differential pressure stickrng.

' Where gasiform fluid is used as the drilling fluid, heretofore the bit cuttings recovered were so small'in size that they were of substantially reduced value for geologic examination and interpretation. This occurred because the cuttings dislodged by the bit were reground under the bit and/or milled between the drill collars and the wall of the hole where there was only small clearance. In the practice of the present invention, both of these disadvantages are diminished or overcome because the higher fluid velocity assures rapid removal of the cuttings from below the bit and rapid transit below the collars. Moreover, since the area of collar surface contacting the wall is small, regrinding is also diminished.

It will be clear that the drill collar of the present invention is quite advantageous and useful.

The nature and objects of the present invention having been completely described and illustrated and the best mode and embodiment contemplated set forth, that I wish to claim as new and useful and secure by Letters Patent is:

1. A drill collar comprising an elongated member adapted to be threadedly arranged in and form part of a rotatable drill string employed in drilling a well and provided with longitudinally and radially extending fins forming a cross in horizontal cross section, each fin being perpendicular to the next fin, said fins extending continuously substantially the length of said member and having an outer cutting surface on the periphery thereof, said fins extending radially a distance slightly less than the gauge of said well, said member having a continuous axial fluid passageway extending therethrough, said fins having a cross-sectional thickness within the range from about half to about twice the diameter of said fluid passageway, the spaces between adjacent fins providing passageways for fluid and providing a space between the wall of the well drilled by said drill string substantially equal to a ratio of horizontal cross-sectional area of said drill collar to the gauge of said well within the range from about 3:1 to about 15:1.

2. A drill collar in accordance with claim 1 in which the outer cutting surface of said fins is provided with a facing of hard, abrasive material.

3. A drill collar in accordance with claim 2 in which the facing is tungsten carbide.

4. A drill collar in accordance with claim 1 in which the outer surface of said fins is convex relative to the axis of said member.

5. Adrill collar in accordance with claim 1 in which the fins extend radially a distance from about A" to about less than the gauge of said well.

6. A drill collar in accordance with claim 1 in which the bottom surface of said fins is provided with a cutting surface.

7. A drill collar in accordance with claim 6 in which the cutting surface on the bottom of said fins is provided with a facing of hard, abrasive material.

References Cited UNITED STATES PATENTS 1,673,924 6/ 1928 Snyder 51-245 2,657,907 11/1953 Cochran 406 X 2,904,313 9/1959 Wisenbaker 175406 3,051,255 8/1962 Deely 175406 X 3,250,578 5/1966 Lubbes 308-4 3,285,678 11/1966 Garrett 308-4 CHARLES E. OCONNELL, Primary Examiner. NILE C. BYERS, Examiner. 

1. A DRILL COLLAR COMPRISING AN ELONGATED MEMBER ADAPTED TO BE THREADEDLY ARRANGED IN AND FORM PART OF A ROTATABLE DRILL STRING EMPLOYED IN DRILLING A WELL AND PROVIDED WITH LONGITUDINALLY AND RADIALLY EXTENDING FINS FORMING A CROSS IN HORIZONTAL CROSS SECTION, EACH FIN BEING PERPENDICULAR TO THE NEXT FIN, SAID FINS EXTENDING CONTINUOUSLY SUBSTANTAILLY THE LENGTH OF SAID MEMBER AND HAVING AN OUTER CUTTING SURFACE ON THE PERIPHERY THEREOF, SAID FINS EXTENDING RADIALLY A DISTANCE SLIGHTLY LESS THAN THE GAUGE OF SAID WELL, SAID MEMBER HAVING A CONTINUOUS AXIAL FLUID PASSAGEWAY EXTENDING THERETHROUGH, SAID FINS HAVING A CROSS-SECTIONAL THICKNESS WITH THE RANGE FORM ABOUT HALF TO ABOUT TWICE THE DIAMETER OF SAID FLUID PASSAGEWAY, THE SPACES BETWEEN ADJACENT FINS PROVIDING PASSAGEWAYS FOR FLUID AND PROVIDING A SPACE BETWEEN THE WALL OF THE WALL DRILLED BY SAID DRILL STRING SUSBTANTIALLY EQUAL TO A RATIO OF HORIZONTAL CROSS-SECTIONAL AREA OF SAID DRILL COLLAR TO THE GAUGE OF SAID WELL WITHIN THE RANGE FROM ABOUT 3:1 TO ABOUT 15:1. 